1. Field of the Invention
The invention relates to a Reed-Solomon type error correcting device and an optical reading apparatus comprising such a device. The invention is applied especially within the framework of error correction in magneto-optic or optical disk reading apparatus.
2. Related Art
Reed-Solomon type error correction (RS) is used in numerous applications. One of the most widespread applications is the compact disk (CD). In the future, RS codes will likewise be used within the framework of the disks referred to as xe2x80x9cDVDxe2x80x9d.
Although developed in the 1960""s, RS codes were not used in apparatus for the general public until the beginning of the 1980""s. This was due in part to the fact that this error correction requires a relatively substantial, and therefore costly, amount of computer power. The correction requires for example multiplication and division of polynomials as well as determination of the roots of polynomials. Within this framework, it is of interest to reduce the calculation time and to reduce the complexity of the circuits applied in this correction, with a view toward reducing cost and increasing reliability.
The object of the invention is a Reed-Solomon type coder-decoder comprising: a generator of syndromes for receiving a data flow and for providing a polynomial of syndrome and a polynomial of erasure; means of implementing Euclid""s algorithm to receive said polynomials of syndrome and erasure and for providing error localization; means of correction for correcting, where applicable, the error or errors in the data flow with the aid of the polynomial of error localization; and in which the means of implementation include first and second registers for storing two intermediate polynomials of location and of evaluation of error, characterized in that the registers are divided into elementary cells set in series and comprising means of multiplexing and of calculation so that during a cycle of a clock signal when a calculation is carried out, it is subsequently possible simultaneously to reverse the data between the two registers.
The means of implementation are preferably arranged to implement the product of the polynomial of error localization and of a polynomial of erasure to obtain a new polynomial of error localization.
The extended Euclid algorithm necessitates the multiplication of polynomials. According to the invention, this fact is advantageously utilized to implement other multiplications of polynomials necessary for the error correction, which permits simplifying the other parts of the correction device.
According to one embodiment of the invention, the means of determination of the coefficients are arranged to implement the product of a polynomial of syndromes by the polynimial of erasure.
The invention also has as its object an optical disks reader comprising the correction device.